sql - 如果已包含数据，则不允许空值更新列

Question

我有一个来源，我从中提取数据以更新现有表。

是否只有在源数据不是时才更新每个字段中的值NULL？

Answer 1

你应该使用ISNULL(@paramA, ColumnA)：

UPDATE someTable
set ColumnA = ISNULL(@ParamA, ColumnA)
WHERE
.....

Answer 2

考虑到你提到如果源数据不为空然后更新

--Create a sample table

DECLARE @SAMPLE TABLE
(
SourceID INT IDENTITY(1,1),
SourceData NVARCHAR(255)
)

--Create dummy data

INSERT INTO @SAMPLE VALUES ('SOMETHING')
INSERT INTO @SAMPLE VALUES (NULL)
INSERT INTO @SAMPLE VALUES ('SOMETHING')


--update source data that is not null, this will update entire table

UPDATE @SAMPLE
SET SourceData = 'New Data'
FROM @SAMPLE t1
INNER JOIN (
SELECT * FROM @SAMPLE Where SourceData is not null) t2 
ON t1.SourceID = t2.SourceID

或者，如果您只想更新选定的记录

--Pass in your variable

DECLARE @SourceID INT

--play around your source id

SET @SourceID = 2

--if the particular id is with null data, then update will never perform

IF EXISTS(SELECT 1 FROM @SAMPLE WHERE SourceID = @SourceID and SourceData is not null)
Update @SAMPLE
set SourceData = 'New Item'
where SourceID = @SourceID